Justification:
Listed as Vulnerable because the extent of occurrence is less than 20,000 km2, the range is severely fragmented, and there is a continuing decline in extent of occurrence and area of occupancy.

The species might also meet Criterion C1 for Vulnerable. There may be <10,000 mature individuals and the continuing decline may be >10% over three generations (i.e., 12 years). The continuing decline, however, has to be estimated, not inferred or projected, requiring quantitative evidence, and evidence for a 10% decline over the next 12 years is not currently available.

The Quokka is endemic to the south-west of Western Australia, Australia, including Rottnest and Bald Islands. The most northern known location is in state forest/water catchment south-east of the Perth metropolitan area. The most inland population is in Stirling Range National Park and its eastern-most known occurrence is at Green Range. The last record from the Leeuwin-Naturaliste National Park is from 1979 and Quokkas are thought to be absent from the Swan Coastal Plain, although there are two unconfirmed reports of presence (de Tores et al. 2007).

This species was formerly distributed on the mainland from Moore River (100 km north of Perth) to the vicinity of Waychinicup National Park on the south coast (de Tores et al. 2007). Kabay and Start (1976) recorded Quokka bones in surface deposits from several sites along the south coast as far east as Fitzgerald River National Park. It was abundant in the Albany district in the 1850s and in the Busselton/ Margaret River area until the late 1920s (White 1952), and was regarded as a problem to pine seedlings in new plantations around Mundaring in the early 1930s (L. Talbot pers. comm.). The distribution at European settlement (about 150 years ago) has been calculated by de Tores et al. (2007) to have encompassed an area of approximately 41,200 km2. The current extent of occurrence is estimated to be about 17,900 km2.

This species is sparsely scattered within abundant suitable habitat (de Tores 2008). The total global population estimated to be 7,850-17,150 mature individuals.

It is difficult accurately to quantify total population trend, but the species is probably decreasing. Quokkas have declined in the northern Jarrah forest, populations in the southern forests might be decreasing due to the presence of introduced pigs, and some populations have disappeared from the extreme south-west of their mainland range. Although numbers fluctuate, the island subpopulations appear to be stable, and the population along the South Coast appears to be increasing in response to fox control.

Because knowledge of Quokka populations varies in different parts of its range, each is listed with a separate population estimate followed by a description of how the estimate was derived.

Rottnest Island (1,700 ha).The population on Rottnest Island has been studied in detail for several decades because of the presence of a University of Western Australia research station there. Much of the pioneer work on marsupial nutrition, reproduction, temperature regulation, immunology, disease, ecology, and behaviour was conducted on the Rottnest Island Quokka population.

Population estimates for Rottnest vary between 4,000 and 17,000, with most estimates at the lower end of this range. The population is known to fluctuate widely. A precautionary population estimate for Rottnest, including uncertainty, would be 4,000 to 8,000 total individuals.

Bald Island (800 ha).Studies on the Bald Island population are much more limited, and there is no recent, published estimate for the island. Tony Friend (pers. comm.), who has worked on Bald Island extensively in recent years, suggests the population is about 2,000. A precautionary population estimate for Bald Island, including uncertainty, would be 500 to 2,000.

Northern Jarrah forest (north of the Preston River).In this region, there have been some populations which have gone extinct in the last 20 years. The presence of pigs has also been recorded at many of the northern Jarrah forest sites and Quokka presence is often detected through non-target captures during pig control programs. Recent research revealed several small subpopulations (between 10 and 48 that were rarely >30 individuals), totalling about 150 animals and declining (Hayward 2005; Hayward et al. 2003, 2004, 2005). Genetic research also has shown that gene flow between subpopulations is rare (Alacs 2001).

Southern forests (south of Collie south and east to Hay River).The average population size in the southern forests is unknown. Anecdotal evidence suggests these southern forest sites support substantially larger populations than the northern Jarrah forest. Recent rapid survey of 1,239 potential Quokka habitat sites by the Department of Environment and Conservation staff revealed evidence of Quokka at 564 of these. Further work is needed to verify the rapid survey technique and examine subpopulation size. A precautionary estimate might be 2,000 to 5,000.

South Coast (from Hay River east to Green Range).There are no overall estimates for the population along the South Coast. There have been recent extensive searches of this area targeting Gilbert’s Potoroo (Potorous gilbertii). During this work many Quokka subpopulations were located. Quokkas are more likely to be increasing rather than declining along the South Coast, which is based on trapping data and observations at Two Peoples Bay (T. Friend pers. comm.). Trapping data indicate a significant increase on Mount Gardner between 1995 and 2001 (after 2001 Quokka excluders were used on Sheffield traps to prevent them from entering potoroo traps and injuring themselves, which led to fewer Quokka records). Sightings of Quokkas in the lower parts of the reserve have increased markedly since 1999 following fox control, with Quokkas now inhabiting dense bush near the picnic area behind the beach and regularly showing themselves to visitors (T. Friend pers. comm.).

In addition, a hair-arch survey of Boulder Hill/Mount Manypeaks/Waychinicup/Cheynes Beach in 2002 produced evidence of Quokkas at 12 out of 13 sites surveyed. Quokkas have found in recent years on the Western Shield transect line in the Stirling Range National Park. They also persist in the Green Range, where there is no fox control (based on Quokka hair recoveries at 3 out of 5 sites surveyed, followed by successful trapping at 2 out of the 3 sites, work carried out in 2001) (T. Friend pers. comm.).

Total numbers in the South Coast region are not known, but are estimated at 1,200 to 2,000 individuals (T. Friend pers. comm.).

This species uses a variety of habits. On Rottnest Island it lives in thickets and scrub habitat. On the mainland, many populations are found close to water (creeks and swamps). In the Jarrah forest, Quokkas are closely associated with the tea-tree (Taxandria linearifolia) in a habitat mosaic of trees at differing ages as determined by fire (Hayward et al. 2007; de Tores 2008). Vegetation is used as cover for nocturnal foraging. Family groups exhibit overlapping home ranges that reflect a general non-territoriality. Exceptions may be made during hot summer periods where males will fight enthusiastically for possession of the best shelters, possibly a limiting factor (Maxwell et al. 1996). Quokka biology data suggest that the generation time is about four years.

Island populations fluctuate, but are stable over the long term. Habitat clearing and the introduction of foxes and feral cats has led to a past decline of mainland populations. Fox control has led to an increase in numbers in some areas but not in others. Feral pigs are causing habitat degradation and excluding Quokkas from swampy areas. Prescribed burning and clearing are a problem in much of the forested habitats.

The Quokka occurs in a number of protected areas and is listed as threatened species under Australian law. Research into subpopulation size and structure, diet, and habitat use has been completed for the northern Jarrah forest. Adaptive management of northern populations is underway. Rapid survey of southern forest subpopulations has been conducted, but further work is needed to define subpopulation size and movements between habitat areas. Feral pig surveys has been conducted in many locations, but additional feral pig control is required. Fox control programs should be maintained.

Hayward, M. W., de Tores, P. J., Augee, M. L., Fox, B. J. and Banks, P. B. 2004. Home range and movements of the quokka Setonix brachyurus (Macropodidae: Marsupialia), and its impact on the viability of the metapopulation on the Australian mainland. Journal of Zoology (London) 263: 219-228.